In practice filling compounds are produced by dispersing pigments and extenders in solvent-containing binders drying physically in oxidative manner or undergoing chemical curing. In view of the fact that such filling compounds have very high viscosities of the order of 15,000 mPas to more than 100,000 mPas, it has been necessary so far to use for their production special dispersing units, i.e. so-called three-cylinder mills (see Dr. Hans Kittel, Lehrbuch der Lacke und Beschichtungen, published by W. A. Colomb as part of the Heeneman GmbH, 1976, vol. IV, page 64).
However, these dispersing processes cause large amounts of solvent vapours to be discharged into the air, as a result of which they act as environmental pollutants. Dispersal with the aid of modern sand mills or bead mills, which being closed-cycle systems do not allow any solvents or only very small amounts thereof to escape into the environment, has not been possible in the past owing to the high viscosity of the filling compounds. It is difficult, uneconomical and also environmentally polluting to dilute the filling compounds to lower viscosities with a view to their dispersal by means of bead mills or sand mills followed by evaporation of the solvents, since disposal of the evaporated solvents entails the expenditure of energy and the production of noxious liquid or gaseous substances. Dispersal of the pigments and extenders solely with the aid of so-called dissolvers results in products the quality of which is far below the standards required of filling compounds suitable in particular for automobile repairs.